This invention relates to an antenna positioning system, and more particularly, to low profile antenna positioning systems for controlling azimuth and elevation angles within a radome.
Antenna positioning systems have been around for as long as there have been signals to send or receive. Even the most simple communications system requires some method of pointing an antenna to obtain desired results from the system. An antenna positioning system often includes some method of pointing, varying or controlling the position of an antenna about an azimuth axis, typically a vertical axis, and about an elevation axis, typically a horizontal axis. In a common system, a yoke is pivotally secured to opposing sides of an antenna so that the antenna pivots about an elevation axis, which typically passes through the locations of pivotal attachment. The yoke is also pivotally mounted to a base directly over the azimuth axis. The yoke, and therefore the antenna, may be rotated about the azimuth axis to control the azimuth angle of the antenna, and the antenna may be rotated about the elevation axis to control the elevation angle of the antenna. Means for determining the position of the antenna relative to a base or mounting surface are often provided, together with means for actuating or moving the antenna through a range of azimuth and elevation angles. Such antenna positioning systems work well for their intended purposes and have benefits associated with their ease of construction and simplicity of operation. These antenna positioning systems are not, however, without problems. For example, these structures tend to be relatively tall, so they do not lend themselves to use in situations in which size, particularly height, is a concern.
Placing antennas within radomes on moving objects is also known. When an antenna positioning system is to be used on a moving object, such as an aircraft or vehicle, the system is typically placed within a radome which is transparent to the signal being sent or received. The radome protects the system from damage while reducing aerodynamic drag that might otherwise hinder operation of the aircraft or vehicle. Particularly when such a system is used on an aircraft, it is important to minimize the size of the radome to reduce aerodynamic drag. It is also desirable to use an antenna positioning system that provides for movement through a wide range of azimuth and elevation angles while providing the largest antenna that can be fit within the radome. Antenna positioning systems have, to date, made poor use of the volume available inside the radome. This has required unnecessarily small antennas or unnecessarily large radomes to be used. For example, if an antenna and yoke are disposed at the azimuth axis, above an azimuth motor and encoder, the radome must be quite tall to accommodate the maximum height of the antenna as it moves through a range of elevation angles. Conversely, if the antenna and yoke are moved far enough away from the azimuth axis so that the antenna may pivot about the yoke over a range of elevation angles, the antenna must be quite short because of the reducing width of the radome as one moves along a radius away from the center.